1. Field of the Invention
This invention relates, generally, to devices that protect a telephone system inside a building from electrical disturbances that occur outside the building. More particularly, it relates to improvements in a five pin building entrance surge protection module.
2. Description of the Prior Art
The National Electric Code requires the telephone industry to provide electrical surge protection at the point of entry where copper wires enter a building. The code requires that telephone equipment within the building be protected from three types of electrical hazards: 1) surge protection from lightning and switching surges; 2) over current protection; and 3) circuit lock-out protection for use in the event a disturbance remains on the circuit for an extended period of time.
The required protection is provided by installing a building entrance panel at the point where the outside lines enter the building. The panel includes a surge protection module for each telephone circuit in the building so that each interior telephone circuit is protected from external electrical disturbances. The panel further includes a means for overcurrent protection and a circuit lock-out means.
The well-known surge protection module has five (5) pins. Two of the pins are in electrical communication with the customer""s telephones and three of them are in electrical communication with power supplied by a utility company.
There are a number of shortcomings with the modules now in use. One of the main drawbacks is that components are designed to perform only one function, such as an electrical or a mechanical function. Thus, multiple components are required to perform multiple functions and a large variety of components must be manufactured to handle the differing requirements of differing applications.
In other words, the known surge protection modules are not of modular construction; each of them must be built to a customer""s specifications.
It follows that there is a need for a component that combines multiple functions, thereby reducing the number of components required for a job.
More particularly, customer requirements differ concerning whether or not a gas tube or a solid state arrester is used for a particular installation. The prior art components are either one or the other, i.e., there are no components that can be provided with either type of arrester.
A need has therefore been perceived for a component that can be provided with either type of arrester at the time of its assembly. This avoids a need to make and store two types of components.
Some, but not all, applications require a thermal fail-safe that shorts out the circuit to prevent long-duration fault currents from reaching customer equipment. Some prior art components are thus manufactured to include such thermal fail-safe means, and some are not. Thus it should be understood that the prior art requires a manufacturer to make components having a gas tube arrester and a thermal fail-safe means, a gas tube arrester and no fail-safe means, a solid state arrester having a thermal fail-safe means, and a solid state arrester having no thermal fail-safe means.
Clearly, a design that would obviate the need for these four different configurations would be highly beneficial.
Moreover, some applications require a back-up protective air gap that sparks over (arcs) at a predetermined voltage if the surge arrester fails to limit the surge voltage in time, and some do not. The multiplier effect this has on the number of different types of components that must be manufactured and kept on hand is apparent.
Moreover, some, but not all, components must include a current-limiting device that quickly limits current and prevents damage to customer equipment for long duration high current faults.
Finally, most components will require test points allowing service personnel to determine if a circuit is energized and to analyze other communication problems that occur. However, some customers decline such option; this creates still another inventory problem for the industry.
It is clear, then, that the art currently requires manufacturers to make many different configurations of components, each of which has a different mixture of devices. This creates inventory problems and drives up the cost of the custom-built components.
Another problem that has troubled the surge protection industry involves the positive temperature coefficient resistors used by the industry. Such devices have electrical leads that require soldering when a connection is made. Thus, there is a need for an improved resistor having no electrical leads.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how the art could be improved.
The long-standing but heretofore unfulfilled need for an apparatus that overcomes the limitations of the prior art is now met by a new, useful, and nonobvious invention. The present invention is a telephone circuit surge protection assembly of the type disposed at the entrance into a building having at least one telephone circuit inside said building. Significantly, it is built of modular parts so that said parts can be assembled in any configuration as may be required by a customer. The modular parts include a housing, a first plurality of electrically-conductive pins adapted for electrical communication with power supplied by a remote utility company, a second plurality of pins adapted for electrical communication with said at least one telephone circuit, and a plurality of bores formed in the housing for receiving the pins. In this way, the bores in the housing serve to properly position the pins when a unit is assembled.
A surge protection means is in electrical communication with preselected pins of said first plurality of pins; advantageously, due to the modular structure of the novel device, the surge protection means may be of the gas tube type or of the solid state type. The type used is dictated by the application.
Electrically conductive means are mounted on the housing to provide electrical communication between the first plurality of pins and the second plurality of pins.
A cover holds together the housing, the surge protection means, and additional components of the assembly as well.
The electrically conductive means includes a pair of flat, electrically conductive strips that overlie the housing and which are apertured at their respective opposite ends to engage their respective pins.
The housing has at least one recess formed therein that is sized to snugly receive a positive temperature coefficient resistor therein so that the assembly may be assembled to include at least one positive temperature coefficient resistor. The electrically conductive means is in electrical communication with at least one positive temperature coefficient resistor.
The positive temperature coefficient resistors of this invention are of parallelepiped construction and have no electrical leads extending therefrom as in prior art resistors of the same type. The housing and the recesses formed therein for receiving the resistors eliminates the need for such electrical leads.
The electrically conductive means is provided in the form of a plurality of electrically conductive spring clips that are engaged by respective pins of the plurality of pins. The spring clips are also disposed in electrically conductive relation to at least one positive temperature coefficient resistor.
Each of said spring clips has an xe2x80x9cLxe2x80x9d shape and a first leg of each spring clip is engaged by one of the pins. A second leg of each spring clip is positioned within at least one recess formed in the housing so that the first leg is in electrical communication with a preselected pin and so that the second leg is in electrical communication with at least one positive temperature coefficient resistor.
A pair test point access openings may also be formed in the cover.
The plurality of spring clips includes at least two spring clips having elongate necks formed integrally with the respective first legs of the spring clips, said elongate necks respectively having a bend formed therein remote from the first and second legs to form a test point contact surface. The respective elongate necks are sized so that the respective test point contact surfaces are in registration with the pair of test point openings formed in the cover.
A fail safe device may also be disposed in electrically communicating relation between the electrically conductive strips and the surge protection means.
Moreover, a meltable insulator means may be disposed between the fail safe device and the electrically conductive means; it melts and provides a path to ground if high current appears for a predetermined length of time.
There are also two ways of providing a backup air gap that provides a flashover path to ground when needed.
Advantageously, the pins of the first plurality of pins have a common length that is less than a common length of the pins of the second plurality of pins. The pins of the first plurality of pins are in electrical communication with the telephone circuit, and the pins of the second plurality of pins are in electrical communication with the power supplied by the remote utility company. The difference in respective common lengths ensures that the pins of the first plurality of pins are in electrical isolation from the power from the remote utility company when the plurality of pins are in electrical communication with the remote utility company.
It is the primary object of this invention to provide a modular five pin protection module so that individual customer requirements can be met without requiring manufacturers to make a wide variety of components, each of which has different features.
Another important object is to provide a positive temperature coefficient resistor having no electrical leads.
Other important objects, features, and advantages of the invention will become apparent as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.